Piezoelectric composite materials are known in the art. One such known piezoelectric composite material which comprises an acetal resin, a polymer of high dielectric permittivity, and a piezoelectric powder is disclosed in U.S. Pat. No. 4,128,489 issued in 1978 to I. Seo. This piezocomposite material possesses good formability and elasticity. However, it has a relatively low piezoelectric sensitivity, high dielectric losses, and a low electromechanical coefficient of efficiency.
U.S. Pat. No. 5,796,207 issued in 1998 to A. Safari, et al. discloses a piezoelectric composite material which comprises a directionally oriented piezoelectric material built into a polymer. However, such a material is difficult to manufacture. Furthermore, the material has low mechanical strength, is difficult to polarize, has high dielectric losses, and has high acoustic losses on the boundaries of a piezophase with a polymer matrix. Korean Patent KR 960012732 issued to Y. Kwang-Soo, et al., in 1996 discloses another known material of the aforementioned type is a matrix piezoelectric composite material that comprises silane, polyvinylidene fluoride, and a piezoelectric powder. Disadvantages of the given material consist of relatively low piezomodulus, low coefficient of piezoelectric coupling, and insufficient electromechanical properties.
Latvian Patent No. LV10134 issued in 1994 to I. Aboltina, et al. discloses a matrix piezoelectric composite material based on a ceramic material and an organic polymer of polymethacrylate or polybutylmethacrylate. Disadvantages of the given material consist of a relatively low piezomodulus, a low piezoelectric coupling coefficient, and insufficient electromechanical properties that result from losses of the elastic wave energy in a near-surface region of matrix composites.
Also known in the art are oriented piezoelectric ceramic and ceramic/polymer composites disclosed, e.g., in U.S. Pat. No. 5,796,207 issued in 1998 to A. Safari, et al. In these materials, the ceramic piezoelectric phase is oriented at an angle with respect to the direction of applied stress. Such materials are difficult to manufacture and present a problem for polarization.
Another known matrix piezoelectric composite material, which is based on a polymer and a solid PbTiO3—BiFeO3 piezoelectric filler is described in European Patent Application Publication No. EP0208019 (invented by J. Giniewicz, et al., and published in 1987). Disadvantages of this material consist of a relatively low piezomodulus, a low piezoelectric coupling coefficient, and low electromechanical properties. In addition, these composites have high losses of acoustic energy in the near-surface region of the piezoelement.
Japanese Unexamined Patent Application Publication (hereinafter referred to as “Kokai”) S57-202789 (invented by Kazuhiko Yamomoto, et al., and published in 1982) discloses a matrix piezoelectric composite material based on various polymers, copolymers, and particles of PbZrO3—PbTiO3 piezoceramics. A problem associated with this material is difficulty in selecting a proper polymer or copolymer for a polymer matrix and high losses of acoustic energy in near-surface region of the piezoelement.
Japanese Kokai S56-6487 (invented by Y. Fujimori, et al., and published in 1981) discloses a matrix piezoelectric composite material comprising a fine inorganic ferroelectric powder, a copolymer of acrylonitrile-butadiene, and a copolymer resin of vinylidene fluoride-ethylene trifluoride. Disadvantages of the given material are complicated manufacturing and polarization of the composite.
Also known is a matrix piezoelectric composite material comprising an organic high polymer and particles of a piezoelectric material disclosed in Japanese Kokai H6-154208 (invented by T. Saito, et al., and published in 1994). Disadvantages of the given material are high losses of acoustic energy that occur in near-surface regions of piezoelement because of the specific matrix structure of the composite.